Brochure No. 1557/9 issued by the firm H. Maihak AG of West Germany discloses one such infrared gas analyzer. This analyzer makes use of a radiation-blocking wheel located intermediate the radiation source and the two radiation paths. The blocking wheel has angularly offset portions which respectively block and transmit radiation, and the wheel is rotated so as to alternately block one and then the other of the two radiation paths. Thus there is an alternation between passage of infrared radiation through the cuvette containing the test sample of gas and passage of infrared radiation through the cuvette containing the reference gas sample. The blocking wheel, on the side thereof facing the radiation source, is not provided at the blocking portion or portions thereof with any means for handling the radiation incident upon such blocking portion or portions. Accordingly, when a blocking portion of the blocking wheel blocks one of the two radiation passages, the radiation incident upon such blocking portion is not utilized; half the emitted radiation passes through the unblocked cuvette, whereas the other half is absorbed by the blocking portion of the blocking wheel. Accordingly, the utilization efficiency of the useful radiated energy is only about 50%.
German published patent application DT-OS No. 1,948,193 discloses another infrared gas analyzer. This arrangement includes a source of infrared radiation, a first path for measuring radiation and a second path for reference radiation, a detector for sensing the radiation passing through the paths, and a mirrored radiation-blocking wheel which is rotated so as to alternately block one and then the other of the two radiation paths. Specifically, the radiation emitted by the source is permitted to pass through both radiation paths (e.g., cuvettes) simultaneously, not merely alternately. The radiation emerging from each path is incident upon a respective one of two deflecting mirrors. The mirrored light-blocking wheel is positioned intermediate the two deflecting mirrors. The light-blocking wheel is rotatable between a first position and a second position. In the first position, it receives the light from one of the deflecting mirrors and reflects such light towards the detector; at the same time, it blocks the light reflected from the other deflecting mirror so that such light cannot reach the detector. In the second position, without further reflection it transmits to the detector the light from the one deflecting mirror, while not reflecting towards the detector the light from the other deflecting mirror. With this arrangement, likewise, only about 50% of the useful radiation is used during any one light measurement; the remaining 50% of the useful radiation is simply absorbed by the light-blocking wheel.
Finally, German allowed patent application DT-AS 1,123,139 discloses a third infrared-absorption gas analyzer. In that construction, there are associated with the source two planar deflecting mirrors, forming an angle of about 90.degree. with each other, and located on opposite sides of the source. Accordingly, two distinct radiation paths are established. Radiation travelling along these two paths is first incident upon a radiation-blocking wheel located intermediate the source and deflecting mirrors, on the one hand, and the reference and measuring cuvettes, on the other hand. With this known construction, there is essentially no possibility of utilizing that part of the emitted radiation which is incident upon the blocking portion of the radiation-blocking wheel.